1. Field of the Invention
The present invention relates to an optical barrel to manually operate or electrically drive an operation ring for operating a focus, a zoom, an iris, or other lens, respectively.
2. Related Background Art
Conventionally, such an optical barrel has been installed with a driving unit in order to operate an operation ring electrically. The operation ring can be operated both electrically and manually. Such driving unit comprises a driving motor for electrical operation; a driving power transmission mechanism for transmitting the driving power of the driving motor to the operation ring; and a driving power interruption mechanism for interrupting the transmission of the driving power to the operation ring in order to perform the manual operation thereof.
Generally, when the operation ring is electrically driven, it is necessary to rotate the ring with a lower load for the improvement of the rotational speed of the operation ring, as well as for the lower dissipation of electric power required for driving the driving motor. In contrast, there is a need for the provision of an appropriate load given to the operation ring so as to facilitate the operation thereof when the operation ring is manually operated. However, if the structure is arranged so that the operation ring is rotatable with a lower load, there is a possibility that the operation ring will rotate easily just by a slight touch. As a result, it is difficult to operate the operation ring smoothly at an extremely slow speed. With a view to solving such a problem, a highly viscous grease, a friction member, or the like has been inclusively installed for the sliding portion of the operation ring, so that a load is given to the operation ring in accordance with the conventional art.
On the other hand, there is disclosed an optical barrel in the specification of Japanese Patent Laid-Open Application No. 7-310769, which is capable of controlling loads needed for the zooming operation that should be carried out in good condition with respect to the zoom lens for a large camera used for a television broadcasting station.
However, these conventional devices make it considerably difficult to incorporate such mechanism in a lens barrel having limited space, such as adopted for use of a handy lens, because the structure of these devices becomes inevitably larger for providing the loads of the operating power for them.